In this first version I made a decision to display closed captioning when the volume is muted, but with the right visualization we should be able to find a nice place for a ToggleButton.  Here is a list of a few other things I did to the project.

• Updated Xml parsing to support markers with multiple types (Marker, CC, etc)
• Converted speaker button control to ToggleButton to display a different visualization when the player is muted.
• Linked volumeSlider to speaker button so slider drops to zero on mute and back to previous volume when mute is turned off.
• Added a new event from mediaControl that is fired when the volume is changed.  This allows the player to control closed captioning display and not the media controller.
• Wrote closedCaptioning UserControl that visualizes the scrolling captions.